1. Field of the Invention
This invention relates to an electrically driven speaker and speaker system used in various audio systems, especially a speaker appropriate to be used for mounting in a casing of a small-size equipment and a speaker system to be constituted with a speaker mounted in a casing.
2. Description of the Related Art
An electrically driven speaker is used generally in various audio systems, up to now. An electrically driven speaker has two types according to magnetic circuit structures, i.e., an outer magnet type and an inner magnet type defined by a magnet position in a magnetic circuit. However, respective vibrating member of two-type speakers has almost same structural relation for a magnetic circuit.
An electrically driven speaker, a half-section shown in FIG. 9, is provided with an outer-magnet-type magnetic circuit comprising an annular top plate 1 having an opening 1a in the center, an annular magnet 2 attached to a bottom surface of the top plate 1 and magnetized in a direction of thickness, and a yoke 3 attached to a bottom surface of the magnet 2. The yoke 3 is provided with a bottom plate 3a, and a center pole 3b projecting from the center of the bottom plate 3a and forming a gap G between an inner circular surface of the opening 1a in the top plate 1.
In FIG. 9, mark 5 shows a frame attached to a top surface of the top plate 1, mark 6 shows a voice coil supported in the magnetic gap G and vibrating correspondingly to electrical signals, mark 7 shows a cylindrical voice coil bobbin transmitting driving force generated in the voice coil 6 to a vibrating system, mark 8 shows a vibrating member attached to a top edge of the voice coil bobbin 7, mark 9 shows a damper joined at an inner circular portion thereof to an intermediate position of the voice coil bobbin 7 and joined at an outer circular portion thereof to the frame 5, and mark 10 shows a roll-shape edge joined at an inner circular portion to an outer circular portion of the vibrating member 8 and joined at an outer circular portion thereof to the frame 5. The voice coil 6, the voice coil bobbin 7, the vibrating member 8, the damper 9 and the edge 10 constitute a vibration system 12.
In the speaker by prior art, constituted above, a space A enclosed with the cylindrical voice coil bobbin 7; describing in detail, a space A formed by a top surface of the center pole 3b, an inner circular surface of the voice coil bobbin 7 and a bottom surface of the vibrating member 8; is ventilated through a thin gap g1 formed by an outer circular surface of the center pole 3b and an inner circular surface of the voice coil bobbin 7 to a space B formed by an outer circular surface of the center pole 3b, a top surface of the bottom plate 3a, an inner circular surface of the magnet 2, and a bottom surface of the top plate 1. Further, the space A is ventilated through a thin gap g2 formed by an inner circular surface of the top plate 1 and an outer circular surface of the voice coil bobbin 6, and a ventilating opening 5a provided in the air-permeable damper 9 and in the frame 5 to an outside of the frame 5, i.e. an outside space of the speaker.
When the above structured speaker is inputted with a large power, a large electric current runs in the voice coil 6 so as to be heated. The heat, generated in the voice coil, is transmitted through air of a space between an outer circular surface of the center pole 3b and an inner circular surface of the voice coil bobbin 7 to the center pole 3b, and transmitted through air of a space between an inner circular surface of the top plate 1 and an outer circular surface of the voice coil 6 to the top plate 1, and then refrigerated. Furthermore, the heat is also refrigerated by air moving in the thin gap g2 formed by an inner circular surface of the top plate 1 and an outer circular surface of the voice coil 6. However, the heat conductivity of air is low and ventilation between the space A and an outside space of the speaker is done through the thin gap g1 formed by an outer circular surface of the center pole 3b and an inner circular surface of the voice coil bobbin 7 so that the ventilation is not enough to refrigerate sufficiently the heat of the voice coil 6. Therefore, electric resistance of the voice coil 6 increases by heating and electric current goes down then sound pressure corresponding to electric input can not be given.
On driving a speaker, expansion and compression of air in the space A is repeated. When driving a speaker by low frequency range with a large input, insufficient ventilation of air causes increasing expansion/compression coefficient of air so that restraining the amplitude of the speaker reduces playback sound pressure and causes sound distortion by non-linearity of air compliance.
It is proposed on a speaker to provide a throughhole C, as shown in FIG. 9, through the center of a center pole 3b, extending from a top surface of the center pole 3b to a bottom surface of a bottom plate 3a, communicating between a space A and an outside of a magnetic circuit, to improve releasing heat generated in a voice coil 6 and transmitted to a center pole 3b for reducing temperature rising of the voice coil 6 and increasing allowable input power. According to this proposed speaker structure, ventilation between a space A and an outside of a magnetic circuit is done through the throughhole so that the expansion/compression coefficient of air is decreased and then sound distortion by non-linearity of air compliance is restrained.
In an inner-magnet-type magnetic circuit as shown in FIG. 10, a cylindrical magnet 31 is provided on a center of a top surface of a bottom plate 30a forming a bottom portion of a bottomed cylindrical yoke 30 and a disk-shaped pole piece 32 forming a magnetic gap G between an inner circular surface of the yoke 30 is joined on the magnet 31. The inner-magnet-type magnetic circuit is provided with a throughhole C through the pole piece 32, the magnet 31 and yoke 30, communicating between a space A and an outside of a magnetic circuit, to improve releasing heat, generated in a voice coil 6 and transmitted to the pole piece 32, for reducing temperature rising of the voice coil 6 and increasing allowable input power so that the expansion/compression coefficient of air is decreased and then sound distortion by non-linearity of air compliance is restrained.
With popularization of a mobile telephone as a small equipment, miniaturization, weight saving, low pricing and higher performance for a mobile phone are required more and technology development regarding the requirements is a mainstream. Study not only on a speaker itself but also a method for mounting a speaker on a casing are required and then a speaker system constituted with a casing applies a structure shown in FIG. 11.
A speaker is shown simply with a vibration system and a magnetic circuit in FIG. 11 and mounted to be held between inner surfaces of a casing 20 by facing a surface of the vibration system 4 and a bottom portion of the magnetic circuit 12 respectively to inner surfaces of the casing 20. Specifically, a sounding surface of the vibration system 4 is placed to abut on an inner surface of a front wall 21, having a sounding opening 21a, of the casing 20 and is pressed by an elastic-material-made pad 23 inserted between an inner surface of a rear wall 22, parallel to the front wall 21, of the casing 20 and a bottom surface of the speaker magnetic circuit 12 so that the speaker is mounted and fixed in the casing. In case, pressing the bottom surface of the speaker magnetic circuit 12 directly by the inner surface of the rear wall 22 of the casing 20, as shown in FIG. 12, the speaker is mounted and fixed in the casing.
Objects to be Solved
As mentioned above, a casing for mounting a speaker is miniaturized and a structure which a speaker is mounted in a casing to be held between inner surfaces by facing a surface of a vibration system and a bottom portion of a magnetic circuit respectively to the inner surfaces of the casing, as shown in FIG. 10 or 11, is applied so that a throughhole, formed in a magnetic circuit to communicate with a space enclosed with a voice coil bobbin, is blocked at a bottom portion of a magnetic circuit by the pad 23 or the inner surface of the rear wall 22. Therefore, air in a space A enclosed with a voice coil bobbin can not be ventilated through a throughhole C from a bottom portion of a magnetic circuit 12.
Thereby, the throughhole C can not perform the function to restrain sound distortion by non-linearity of air compliance by improving releasing heat, generated in a voice coil 6 and transmitted to the pole piece 32, for reducing temperature rising of the voice coil 6 and increasing allowable input power.
This invention has been accomplished to overcome the above drawbacks and an object of this invention is to provide a speaker enabled to ventilate air in a space enclosed with a voice coil bobbin to outside of a magnetic circuit through a throughhole formed in the magnetic circuit to communicate with the space even if the speaker is mounted and fixed between inner surfaces in a casing to face a surface of a vibration system and a bottom portion of the magnetic circuit respectively to inner surfaces of the casing.
Another object is to provide a speaker system enabled to ventilate air in a space enclosed with a voice coil bobbin to an outside of a magnetic circuit through a throughhole formed in the magnetic circuit to communicate with the space even if the speaker is mounted and fixed between inner surfaces in a casing to face a surface of a vibration system and a bottom portion of the magnetic circuit respectively to inner surfaces of the casing.
How to Attain the Object
In order to attain the objects, according to an aspect of this invention, there is provided a speaker which includes a vibration system having a voice coil, a cylindrical voice coil bobbin carrying said voice coil and a vibrating member attached to said voice coil bobbin, and a magnetic circuit generating magnetic force in cooperating with the voice coil to drive said vibrating member, a throughhole formed through said magnetic circuit to communicate with a space enclosed with the voice coil bobbin for ventilating air in said space from a bottom portion of the magnetic circuit; for being used to be fixed between inner surfaces of a casing by facing a surface of the vibration system and a bottom portion of the magnetic circuit respectively to the inner surfaces, and comprises an air path formed in the magnetic circuit to communicate with said throughhole for ventilating air in the space to outside of the magnetic circuit.
In the above-mentioned structure, air in the space enclosed with the voice coil bobbin can be ventilated to outside of the magnetic circuit through the air path formed in the magnetic circuit to communicate with the throughhole for ventilating air in the space from a bottom portion of the magnetic circuit so that air in the space can be ventilated to outside of the magnetic circuit even if the throughhole is blocked by fixing between the inner surfaces of the casing to face the surface of the vibration system and the bottom portion of the magnetic circuit respectively to the inner surface.
According to another aspect of the invention, there is provided a speaker which comprises a speaker as referred to above, wherein said air path is formed in the bottom portion of said magnetic circuit.
In the above-mentioned structure, air ventilation through the air path is kept even if the bottom portion of the magnetic circuit is pressed with any members for fixing between inner surfaces of the casing. So it is no chance that air in the space cannot be ventilated to outside of the magnetic circuit caused by blocking the throughhole.
According to yet another aspect, there is provided a speaker which comprises a speaker as referred to above, wherein said air path is formed, in the bottom portion of the magnetic circuit, extending to an outer edge of the bottom portion of the magnetic circuit.
In the above-mentioned, air ventilation through the air path, formed in the bottom portion of the magnetic circuit extending to an outer edge of the bottom portion of the magnetic circuit, is kept even if the bottom portion of the magnetic circuit is pressed with any members for fixing between inner surfaces of the casing. So it is no chance that air in the space cannot be ventilated to outside of the magnetic circuit caused by blocking the throughhole.
According to further aspect of the invention, there is provided a speaker which comprises a speaker as referred to above, wherein said air path is formed, in the bottom portion of the magnetic circuit, extending to an area of the bottom portion of the magnetic circuit which can not be blocked by the inner surfaces of the casing.
In the above-mentioned structure, air ventilation through the air path, formed in the bottom portion of the magnetic circuit extending to an area of the bottom portion of the magnetic circuit which can not be blocked by the inner surfaces of the casing, is kept even if the bottom portion of the magnetic circuit is pressed with any members for fixing between inner surfaces of the casing. So it is no chance that air in the space cannot be ventilated to outside of the magnetic circuit caused by blocking the throughhole.
According to further aspect of the invention, there is provided a speaker which comprises a speaker as referred to above, wherein said magnetic circuit is outer-magnet-type and said throughhole is formed extending to the bottom portion of the magnetic circuit through a center pole of said magnetic circuit.
In the above-mentioned structure, air ventilation through the air path, formed in the bottom portion of the magnetic circuit, is kept even if the bottom portion of the magnetic circuit is pressed with any members for fixing between inner surfaces of the casing. So it is no chance that air in the space cannot be ventilated to outside of the magnetic circuit caused by blocking the throughhole formed extending to the bottom portion of the magnetic circuit through a center pole of the outer-magnet-type magnetic circuit.
According to further aspect of the invention, there is provided a speaker which comprises a speaker as referred to claim 2, wherein said magnetic circuit is inner-magnet-type and said throughhole is formed extending to the bottom portion of the magnetic circuit through a pole piece and a magnet of said magnetic circuit.
In the above-mentioned structure, air ventilation through the air path, formed in the bottom portion of the magnetic circuit, is kept even if the bottom portion of the magnetic circuit is pressed with any members for fixing between inner surfaces of the casing. So it is no chance that air in the space cannot be ventilated to outside of the magnetic circuit caused by blocking the throughhole formed extending to the bottom portion of the magnetic circuit through a pole piece and a magnet of the inner-magnet-type magnetic circuit.
According to further aspect of this invention, there is provided a speaker system which includes a speaker comprising a vibration system having a voice coil, a cylindrical voice coil bobbin carrying said voice coil and a vibrating member attached to said voice coil bobbin, and a magnetic circuit generating, magnetic force in cooperating with the voice coil to drive said vibrating member, and a casing for receiving said speaker, wherein said speaker is fixed between inner surfaces of said casing by facing a surface of said vibration system and a bottom portion of said magnetic circuit respectively to said inner surfaces, wherein a path is formed in said magnetic circuit to communicate with a space enclosed with the voice coil bobbin for ventilating air in said space from a bottom portion of the magnetic circuit.
In the above-mentioned structure, air in the space enclosed with the voice coil bobbin can be ventilated to outside of the magnetic circuit through the path formed in the magnetic circuit even if the speaker, having a vibration system including a voice coil, a cylindrical voice coil bobbin and a vibrating member, and a magnetic circuit, is fixed between the inner surfaces of the casing by facing the surface of the vibration system and a bottom portion of the magnetic circuit respectively to the inner surface. So it is no chance that air in the space cannot be ventilated to outside of the magnetic circuit.
According to further aspect of the invention, there is provided a speaker system which comprises a speaker system as referred to above, and said path provided with a throughhole formed through said magnetic circuit to communicate with a space enclosed with said voice coil bobbin for ventilating air in said space from a bottom portion of said magnetic circuit, and an air path formed, in the bottom portion of the magnetic circuit, to communicate with said throughhole for ventilating air in said space to outside of the magnetic circuit.
In the above-mentioned structure, air in the space can be ventilated to outside of the magnetic circuit through the throughhole formed through the magnetic circuit for ventilating air in the space from a bottom portion of the magnetic circuit and the air path formed in the bottom portion of the magnetic circuit, to communicate with the throughhole for ventilating air in the space to outside of the magnetic circuit. So it is no chance that air in the space cannot be ventilated to outside of the magnetic circuit.
As mentioned above, there is provided a speaker or a speaker system having no chance of disabled ventilating air in a space enclosed with a voice coil bobbin to outside of the magnetic circuit through a throughhole formed in a magnetic circuit to communicate with the space enclosed with a voice coil bobbin, even if mounting a speaker between inner surfaces of a casing, facing a surface of a vibration system and a bottom portion of a magnetic circuit to inner surfaces of the casing.
Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted that various change and modifications can be made with the scope of the present invention. Incidentally, the content of Japanese Patent Application No. 2001-55161 is hereby incorporated by reference.